The decision leaves in place President Obama's 2009 executive order expanding research on stem cells taken from human embryos, which many scientists say has the potential to produce breakthroughs in treatment of numerous conditions, particularly spinal cord injuries, diabetes and Parkinson's disease.

Obama reasoned that research on stem cell lines from embryos created through in vitro fertilization was not ethically problematic. Congress banned the creation or destruction of embryos for research purposes in 1996.

A federal court in Washington, D.C., issued an injunction temporarily blocking the order in August 2010 after two scientists opposed to all embryonic stem cell research, James Sherley of the Boston Biomedical Research Institute and Theresa Deisher of Sound Choice Pharmaceutical Institute, sued on behalf of "plaintiff embryos," contending that Congress had forbidden any research whatsoever on embryonic stem cells.

Since then, federal courts have rejected their contention that the failure of the National Institutes of Health and the Department of Health and Human Services to respond to their arguments rendered Obama's policy illegal.

The Supreme Court made no comment Monday in its one-sentence order rejecting the scientists' appeal.

Embryonic stem cells have been the focus of fierce debate since the mid-1990s. Many scientists see them as a watershed in the treatment of serious ailments because they have the potential to grow into any of the body's cell types, promising the eventual generation of replacement nerve lines and vital organs, including the brain and the heart.

But anti-abortion activists vigorously oppose the research because the cells come from human embryos and days-old human fetuses, which they contend are fully human. Many of them, including Sherley, want to limit research to stem cells derived from adult tissue, which most researchers contend have less potential to transform into other types of cells.

Steven Aden, senior counsel for the Alliance Defending Freedom, a Christian legal center that helped litigate the case, criticized the decision Monday, saying the 1996 law "is clear, and we had hoped the U.S. Supreme Court would uphold its clear intent."

"Americans should not be forced to pay for experiments that destroy human life, have produced no real-world treatments and violate federal law — especially in burdened fiscal times like these," he said.

The Department of Health and Human Services, whose secretary, Kathleen Sebelius, was the named defendant, had no immediate reaction.